Polarizer films with high thermal and hygroscopic stability

ABSTRACT

This invention provides novel liquid crystalline polymers which, when blended with a suitable dye at a suitable high temperature and extruded, yields polarizer films with superior thermal and hygroscopic stability and polarizing efficiency. The invention further provides a process to prepare such polarizer films.\!

BACKGROUND OF THE INVENTION

Polarizers are important components of liquid crystal displays. Liquidcrystal displays (LCDs) are widely used components in applications suchas, for example, Notebook Personal Computers (PCs), calculators,watches, liquid crystal color TVs, word processors, automotiveinstrument panels, anti-glare glasses and the like. Typically,polarizers are used in the form of film, the polarizer film. In an LCD,the liquid crystal elements are generally sandwiched between two layersof polarizing films (also referred to as polarizer film herein) whichregulate the incident light that enters the liquid crystal producing anon-and-off contrast.

The polarizing film comprises a polymeric film, a colorant and otheroptional layers collectively referred to as polarizing film. Thepolymeric film is traditionally a stretched polymer film such as, forexample, polyvinyl alcohol (PVA). The colorant is usually iodine or adichroic dye that is absorbed on the polymer film. This arrangement maythen be coated or sandwiched on both sides with a substrate such as, forexample, polyethylene terephthalate (PET), polymethyl methacrylate(PMMA), triacetyl cellulose (TAC), and the like. This may further becoated with an adhesive layer, protective layer, and the like.

The nature and quality of the polymeric substrate film influences theperformance of the polarizing film. Traditional polymeric film materialssuch as stretched PVA are increasingly found to be inadequate inperformance. Their limitations have become apparent with increasinglysophisticated applications for polarizer films and LCDs. More and more,the environment for use of these materials is becoming increasinglyharsher in terms of temperature, humidity and the like. PVA films lackthe needed heat and humidity resistance, strength, dependability, easeof use and ease of processing. Furthermore, they frequently suffer fromdeterioration of optical properties, such as a decrease in polarizingefficiency when exposed to high humidity/heat environment. Accordingly,improved polarizing films with high thermal and hygroscopic stabilityare urgently required to satisfy increasingly sophisticatedapplications.

Several attempts have been made to improve the performance of polarizerfilms with limited success. U.S. Pat. Nos. 5,310,509 and 5,340,504disclose polarizing films based on water-soluble organic polymers suchas polyvinyl alcohol and dichroic dyes. U.S. Pat. Nos. 4,824,882 and5,059,356 disclose polyethylene terephthalate ("PET") films forpolarizer applications. U.S. Pat. No. 5,318,856 discloses films ofpolyvinyl alcohol, polyvinyl formal, polyvinyl acetal and polyvinylbutyral. U.S. Pat. No. 4,842,781 discloses films of polyvinyls,polyester and polyamides. These polymers, however, still have the samedisadvantages of PVA, especially in thermal and humidity resistance.

U.S. Pat. No. 5,071,906 discloses a polarizing film comprising auniaxially stretched PVA having a degree of polymerization of about2,500-10,000, and a colorant. While this is a slight improvement overtraditional lower molecular weight PVA, it still suffers from thedisadvantages of PVA.

Liquid crystal polymers are known to possess higher thermal stabilitythan traditional thermoplastics. Furthermore, the process of extrusionor molding generally achieves high degree of orientation in liquidcrystal polymers. For this reason, liquid crystal polymers would beideal candidates for polarizer substrate film applications. In fact,some attempts have been made in the past to use such polymers forpolarizer applications. For example, Japanese patent application JP62-28698 (filed Feb. 10, 1987) discloses a polarizing film consisting ofa thermotropic liquid crystal polyester film with a dichroic coloringmatter dyed and oriented, wherein the polymer is a copolyester of ahydroquinone derivative (A), a terephthalic acid ingredient (B), anisophthalic acid ingredient (C) and a parahydroxybenzoic acidingredient, with the molar ratio of A to D being in the range 5:95 to70:30% and the molar ratio of B to C being in the range 50:50 to 100:0%.The disclosed polymer compositions are difficult or nearly impossible tomake. Additionally, the monomer ratios disclosed for those polymers donot necessarily yield a balanced formula for preparing liquidcrystalline polymeric compositions. Moreover, if even one could makesuch polymers, any films from such polymers are likely to besubstantially deficient in optical transparency, which therefore wouldlimit and/or prevent any potential utility as polarizing films,especially in stringent environments.

U.S. Pat. No. 4,840,640 discloses the use of "liquid crystallinepolyethylene terephthalate-parahydroxybenzoic acid," formed bycopolymerizing a polyethylene terephthalate component (A) with aparahydroxybenzoic acid component (B) with the A:B molar ratio being inthe range 40:60 to 5:95. Optical properties, especially lighttransmittance are a concern with such compositions. Additionally, suchcompositions have to be first blended with a dichroic acid and thenformed into a film through a die at a high shear rate to achievesatisfactory film orientation and light transmittance. This not onlyincreases the processing steps, but also still yields films withinadequate performance.

Accordingly, it is an object of this invention to provide a polarizingfilm which has high thermal and hygroscopic stability and is useful forexisting as well as sophisticated applications.

It is another object of this invention to provide a liquid crystalpolymeric film useful for polarizer applications.

It is an additional object of this invention to provide liquid crystalpolymer compositions that can be blended with suitable dyes and thenformed into films useful for polarizer applications.

It is yet another object of this invention to provide liquid crystallinepolymers which can form films with high orientation, opticaltransparency, moisture resistance and heat resistance with minimalprocessing needs, and which can be blended with organic dichroic dyes tobe converted into polarizing films with high thermal and hygroscopicstability.

Other objects and advantages of the present invention shall becomeapparent from the accompanying description and examples.

SUMMARY OF THE INVENTION

One or more of the objects of the invention are achieved by theprovision of an all-organic polarizing film, which film comprises ablend of (a) at least one film-forming, wholly aromatic thermotropicliquid crystalline polymer ("LCP"), and (b) at least one organicdichroic dye compatible with the polymer, wherein said polarizing filmpossesses an initial polarizing efficiency of at least 70%, and furtherwherein said polarizing film substantially retains its polarizingefficiency when exposed to at least 90° C. temperatures and 90% RelativeHumidity ("R.H.") for a period of at least 100 hours. The term"compatible" refers to the fact that the dye and the polymer aresuitable to be blended at a range of temperatures including and up tothe melt of the polymer, and then to be extruded into an uniform film attemperatures up to and including the melt of the polymer to yield thepolarizing film in which the dye molecules are uniformly distributed.The term "substantially retains its polarization efficiency" refers tothe requirement that the initial polarization efficiency of the filmdoes not drop off by more than 10% (of the initial polarizingefficiency) after the film is exposed to the above-noted temperature andhumidity environment for the duration specified above. The preferredblending and processing of the polymer-dye combination is performed attemperatures above 170° C. or at, or near, the melt temperature of thepolymer; therefore, both the polymer and the dye have to possesssufficiently high stability, with no chemical change, to thoseconditions.

The LCP is selected from the group consisting of polyester, polyamide,polyesteramide, polyketone, polycarbonate, polyurethane, polyether,polyvinyl and the like. A preferred LCP is a polyester or apolyesteramide. An illustrative liquid crystalline polymer useful in thepractice of the invention comprises repeat units corresponding to theformula:

    -- P.sup.1 !.sub.m -- P.sup.2 !.sub.n-- P.sup.3 !.sub.q--

wherein P¹ is an aromatic hydroxy carboxylic acid or an aromatic aminocarboxylic acid; P² is an aromatic dicarboxylic acid; P³ is a phenoliccompound; m, n and q represent mole percent of the respective monomersgenerally ranging from 0-70 mole percent individually, with m+n+qtotalling 100 mole %. The preferred value of m is about 0-40%, n isabout 0-40% and q is about 0-30%. In addition to P¹, P² and P³,additional monomeric moieties such as, for example, a second aromatichydroxy carboxylic acid or an amino carboxylic acid -- P⁴ !_(r) --, adiphenol moiety -- P⁵ !_(s), and the like, may be part of the polymerrepeat unit, in which case r is about 5-20 mole %, and s is about 5-20mole %, with the total m+n+q+r+s being adjusted to be 100 mole %. P⁴ isdifferent from P¹ and P⁵ is different from P³. Suitable dichroic dyesinclude, but are not limited to, straight chain dyes, branched dyes,direct dyes, disperse dyes, acidic dyes and the like.

The invention further provides a process to make polymer-dye blends forpolarizer film compositions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment, the present invention discloses an all- organicpolarizing film with high thermal and humidity stability, and polarizingefficiency. The film may possess additional advantages such as highorientation, optical clarity and dichroic ratio. The term "high thermaland humidity stability" refers to no substantial change in opticalproperties of the polarizer film when the film is exposed toenvironmental conditions of at least about 90% humidity and temperaturesof at least about 90° C. for at least about 100 hours. The term "highpolarizing efficiency" refers to polarization efficiency of at least70%.

The inventive polarizing film is obtained from a blend comprising (a)one or more film-forming, wholly aromatic thermotropic liquidcrystalline polymers, and (b) one or more compatible organic dichroicdyes. The organic polymers and dyes suitable to practice the inventionare as stated above. Among the polymers listed, liquid crystallinepolyesters or polyesteramides are preferred. The preferred LCPcompositions comprise the repeat units:

    -- P.sup.1 !.sub.m -- P.sup.2 !.sub.n-- P.sup.3 !.sub.q--

wherein P¹, P², and P³ are as described above. Examples of P¹ include,but are not limited to, monomers such as 4-hydroxybenzoic acid,2-hydroxy-6-naphthoic acid, 4-aminobenzoic acid, and4-carboxy-4'-hydroxy-1,1'-biphenyl. Examples of P² include, but are notlimited to, terephthalic acid, isophthalic acid, phthalic acid,2-phenylterephthalic acid, 1,2-naphthalene dicarboxylic acid,1,4-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid and4,4'-biphenyldicarboxylic acid. Examples of P³ include, but are notlimited to, resorcinol, hydroquinone, methyl hydroquinone, phenylhydroquinone, catechol, 4,4'-dihydroxybiphenyl, bisphenol A, andacetaminophen. Additional monomers such as a second hydroxycarboxylicacid or a second aminocarboxylic acid -- P⁴ !_(r) --, a diphenol moiety,-- P⁵ !_(s) --, and the like, may also be part of the polymeric repeatunit, with r and s being the respective molar quantities of therespective monomer, with P⁴ being different from P¹, and P⁵ beingdifferent from P³. Examples of P⁴ include, but are not limited to,4-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, 4-aminobenzoic acid,and 4-carboxy-4'-hydroxy-1,1'-biphenyl. Examples of P⁵ include, but arenot limited to, resorcinol, hydroquinone, methyl hydroquinone, phenylhydroquinone, catechol, 4,4'-dihydroxybiphenyl, bisphenol A, andacetaminophen. The individual monomers P¹, P², P³, P⁴ and P⁵ are presentin amounts of 0-40, 0-40, 0-30, 5-20 and 5-20 mole percent respectively.The total molar amounts of m+n+q+r+s equals 100%. Still additionalmonomers such as, for example a third diphenol, or another dicarboxylicacid and the like, may also be present in the repeat unit in suitableamounts. In selecting the monomers and their respective quantities, careshould be taken not to sacrifice the desired properties of the polymer.Suitable choice of monomers and their respective amounts leads to thepolymers and thereon to polarizer films with desired thermal andhygroscopy stability and other properties.

The invention may be illustrated by a polarizer film prepared from ablend of (a) the LCP (hereinafter referred to as "COTBPR"), preparedfrom the monomers 4-hydroxybenzoic acid ("HBA") for P¹,6-hydroxy-2-naphthoic acid ("HNA") for P², terephthalic acid ("TA") forP³, 4,4'-biphenol ("BP") for P⁴ and resorcinol ("R") for P⁵ in itsrepeat unit in the ratio 30:30:20:10:10 respectively, and (b) a suitableorganic dichroic dye. Preparation of COTBPR may be done by any knownmethod. In a typical synthesis, the above-noted five monomers in theirrespective mole ratios were mixed in a suitable apparatus containing asuitable distillation head. The contents are kept in an inert atmospherewhile a catalyst such as, for example, potassium acetate, and a solventsuch as, for example, acetic anhydride are added to the ingredients andthe mixture is heated and stirred in an oil bath. The temperature israised high enough for acetic acid to distil over. After almost allacetic acid has been possibly removed, the apparatus is evacuated whenpolymer COTBPR forms as a polymer melt. As any remaining acetic aciddistils over, the viscosity keeps increasing. The apparatus is thencooled to, for example, ambient temperature, when the desired COTBPR isisolated.

The polymer may be analytically characterized by measuring typicalpolymer properties such as inherent viscosity ("I.V."), melt viscosity("MV"), as well as by other techniques such as differential scanningcalorimetry ("DSC"), thermogravimetric analysis ("TGA"), NMR, IR and thelike conventional methods well known to those skilled in the art. I.V.may be defined as:

    I.V.=ln(η.sub.rel)/c

where c is the concentration of solution (0.1 wt %), and η_(rel)=relative viscosity. The relative viscosity may be measured by dividingthe flow time in a capillary viscometer of the polymer solution by theflow time of the pure solvent. An important property is thermalstability. DSC gives a good indication of the glass transitiontemperature (T_(g)). The melt temperature T_(m) is also determined byDSC and is defined as the peak of a melt endotherm shown in the DSC.Since the inventive LCP has to be processed at high temperatures,polymeric composition with high enough T_(g) and T_(m) (preferable nomelt temperature) are preferred. Hot stage optical microscopy measuresthe liquid crystalline phase change and the anisotropy of the melt.

In a typical preparation of COTBPR with the above-noted molar ratios,the polymer had an I.V. of 2.0-2.4 dl/g as determined in apentafluorophenol solution of 0.1 weight percent concentration at 60° C.and a MV of about 700-1,700 poise at a shear rate of 10³ sec⁻¹ measuredat 230° C. in a capillary rheometer using an orifice of 1 mm diameterand 30 mm length. The T_(g) as measured by DSC (10° C./min heating rate)was about 106° C. and the solid-to-liquid crystalline transition(T_(s)→lc) at about 170° C. with the polymer melt being opticallyanisotropic. No T_(m) could be found, showing that the polymer COTBPRpossesses exceptional thermal properties.

By varying the monomers P¹, P², P³, P⁴ and P⁵, and their amounts in thepolymerizations, several LCPs could be prepared, as described in theEXAMPLES section below.

An embodiment of the present invention includes all organic polarizingfilms made with inventive organic polymers, and dichroic dyes, andpossessing high thermal and hygroscopic stability. The inventivepolymers are blended with organic dichroic dyes, to produce acomposition to form polarizing films therefrom. Suitable dichroic dyesinclude, but are not limited to, straight chain dyes, branched dyes,direct dyes, disperse dyes, acidic dyes and the like. Yellow, orange,blue, purple or red dyes are all suitable. Several classes of suitabledyes are well known to those skilled in the art. They include, but arenot limited to azo dyes, anthraquinone dyes, commercially availableDisperse dyes such as Blue 214, Red 60 and Yellow 56, direct dyes suchas Black 17, 19 and 154, Brown 44, 106, 195, 210, 242 and 247, Blue 1,15, 22, 78, 90, 98, 151, 168, 202, 236, 249, and 270, Violet 9, 12, 51,and 98, Green 1 and 85, Yellow 8, 12, 44, 86, and 87, Orange 26, 39, 106and 107, and Methylene violet Bernthsen (available from Aldrich ChemicalCompany, Milwaukee, Wis.). More than one compatible dyes may also beused, if so desired. The choice of suitable dichroic dye or dyes dependson several factors, as is well known to those skilled in the art. Somesuch factors include, but are not limited to, light fastness andmigration in the polymer. Another desirable property is that thetransition moment of the dye and molecule main axes should have the samedirection. Such factors form the "compatibility" requirement discussedearlier.

Polarizing films comprising the inventive polymer-dye combination may beformed any suitable method. For example, the polymer and dye may bephysically blended together at ambient temperature and then convertedinto the film by a suitable method. A preferred method, however, is toblend a mixture of both the LCP composition and the dye at temperaturesof at least 170° C. and upto about, or at, the melt temperature of thepolymer and form the film also at such high temperatures. A still morepreferred method, however, is to melt-blend a mixture of both the LCPcomposition and the dye (blending the two together at temperatures at,or near, the melting temperature of the polymer) prior to film formationinto an extrudable mixture and then extrude the mixture at a suitabletemperature, for example at the melt temperature of the polymer, into afilm. This method takes advantage of the unique high thermal stabilityproperties of the inventive polymer-dye combinations and yields apolarizer film wherein the dye is uniformly dispersed in the polymerfilm. Thus, for example, the above-described COTBPR and a suitable dyemay be taken together in a suitable mixer and heated to a suitabletemperature, in the general range 170°-300° C., and preferred range170°-250° C., and blended thereat to form a well blended mixture. Thismixture may be charged into a suitable melt extrusion apparatus, meltedand the melt then extruded to yield a suitable dimension polarizer film.This process has the added advantage that film dimensions can be easilychanged by changing the extrusion die accordingly. The choice of asuitable dye or dyes has relevance in this process of melt blending andextrusion. Since melt blending and extrusion are at fairly hightemperatures, the dye and the polymer have to possess adequate thermalstability at such temperatures. The inventive polymers fit thatrequirement very well. If the polymer does not have a melt temperature,as many of the inventive polyesters are, the blending and extrusion maybe done at as high a temperature as possible, limited perhaps only bythe thermal characteristics of the dye.

Characterization of the inventive polarizer film may be performed bywell known methods skilled in the art. Polarizer films preparedaccording to the present invention have high thermal and humidityresistance and polarizing efficiency (as measured by the polarizingcoefficient). They also possess excellent optical characteristics suchas light transmittance in the wavelength desired. The desired wavelengthdepends on the dye selected. In a typical experiment, for example, aCOTBPR film prepared as described above was melt-blended with MethyleneViolet Bernthsen dye at about 240° C. and the blend was then meltextruded at temperatures above 200° C. to form a polarizer film. Opticalproperties of this film, including the polarization coefficient, weremeasured according the procedure described in U.S. Pat. No. 5,071,906cited above. The film had a blue color with transmittance of about 40%and an initial polarizing coefficient of about 93% in the wavelengthregion 550-630 nm.

The advantageous high thermal and hygroscopic stability of the inventivepolarizer film was demonstrated as follows. The film was subjected to anenvironment of 100° C. and 95% Relative Humidity ("R.H.") for about 120hours, and the polarizing coefficient was measured again. The polarizingcoefficient stayed at about 92%, indicating virtually no change. Forcomparison, commercially available polarizer films based on both PVA andiodine, and PVA and a dichroic dye were tested under the sameconditions. The polarizing coefficients of these comparative filmsdropped off either totally or substantially after exposure to theabove-noted heat/humidity environment even though they started off withslightly higher initial polarization coefficients. This demonstrated thesuperior thermal/humidity resistance of the inventive polarizer filmscompared to conventional polarizer films.

In addition to offering polarizers with superior properties, the presentinvention allows one to tailor-make polarizer films to suit differentwavelengths. This is done by appropriately selecting the dye or dyes.The preferred process is a melt extrusion; no solvents are generallyneeded. Because of this the dye incorporation and distribution arelikely to be much more uniform than in the conventional solution-dippingprocess. Furthermore, the extrusion temperatures can be easily adjustedto suit different dyes and LCP compositions, depending upon theirthermal stability. Thus the inventive process is much more versatilethan the conventional methods of preparing polarizer films.

The following EXAMPLES are provided to further illustrate the presentinvention, but the invention is not to be construed as being limitedthereto.

EXAMPLES Example 1

Preparation of COTBPR:

This example illustrates the preparation of COTBPR polyester from a 1mole reaction mixture of 4-hydroxybenzoic acid ("HBA"),6-hydroxy-2-naphthoic acid ("HNA"), terephthalic acid ("TA"),4,4'-biphenol ("BP"), and recorsinol ("R") in the ratio 30:30:20:10:10.

To a 500 ml 3-neck flask equipped with a half-moon shaped TEFLON®stirrer blade, gas inlet tube, thermocouple, a Vigreux column attachedto a condenser and receiver were added the following:

a) 41.440 grams of 4-hydroxybenzoic acid (0.3 moles);

b) 56.456 grams of 6-hydroxy-2-naphthoic acid (0.3 moles);

c) 33.226 grams of terephthalic acid (0.2 moles);

d) 18.600 grams of 4,4-biphenol (0.1 moles);

e) 11.012 grams of resorcinol (0.1 moles);

the flask was immersed in an oil bath and provided with means toaccurately control the temperature. The flask was thoroughly purged ofoxygen by evacuation and then flushed with nitrogen three times, andslowly heated in the oil bath; and

f) 0.02 grams of potassium acetate was added as a catalyst along with105.48 grams of acetic anhydride (2.5% excess) . Acetic acid began todistill over and was collected in a graduated cylinder.

The contents of the flask were heated while stirring at a rate of 2000rpm to 200° C. over a period of 60 minutes at which time 10 ml of aceticacid had been collected. The reaction temperature was then graduallyraised at a rate of about 1° C./min to 320° C. at which time 96 ml ofacetic acid had been collected. The flask was heated at 320° C. foranother 60 min. A total of 110.5 ml of acetic acid had been collected.The flask was then evacuated to a pressure of 1.0 mbar at 320° C. whilestirring. During this period the polymer melt continued to increase inviscosity while the remaining acetic acid was removed from the flask.The flask and its contents were removed from the oil bath and wereallowed to cool to the ambient temperature. Polymer was then removedfrom the flask and a total of 120 grams of polymer was obtained.

The resulting polyester had an inherent viscosity (IV) of 2.0-2.4 dl/gas determined in a pentafluorophenol solution of 0.1 percent by weightconcentration at 60° C. and a melt viscosity (MV) of 700-1,700 poise ata shear rate of 10³ sec⁻¹ measured at 230° C. in a capillary rheometerusing an orifice of 1 mm diameter and 30 mm length.

When the polymer was subjected to differential scanning calorimetry (10°C./min heating rate), it exhibited a glass transition temperature (Tg)of 106° C.; no melt endotherm could be detected. When the polymer wasexamined by hot-stage cross-polarized optical microscopy, it had atransition temperature from solid to liquid crystalline (T_(s)→lc) at170° C. The liquid crystalline phase was optically anisotropic.

Examples 2-14

Following the procedure outlined in Example 1, the following additionalvariants of the COTBPR composition were prepared having differentproportions of the five ingredients noted above for COTBPR. Composition,glass transition temperature, melt temperature and I.V. for thecompositions appear in Table I below. Unless otherwise indicated,properties were measured as in Example 1. Table II lists polymers(EXAMPLES 15-23) which are not variants of COTBPR since they includeadditional monomers ("X" in Table II) or exclude some monomers of COTBPR("--" in Table II).

                  TABLE I                                                         ______________________________________                                        Ex-                                      I.V.                                 ample HBA:HNA:TA:BP:R                                                                             Tg °C.                                                                         Tm °C.                                                                       T.sub.S→1C °C.                                                         (dl/g)                               ______________________________________                                        1     30:30:20:10:10                                                                              106     none  170    2.5                                  2     20:30:25:15:10                                                                              108     none  280    2.74                                 3     30:20:25:15:10                                                                              107     none  275    2.12                                 4     40:10:25:15:10                                                                              106     none  255    1.96                                 5     30:10:30:20;10                                                                              111     none  280, 385                                                                             2.64                                 6     20:20:30:20:10                                                                              108     none  350, 385                                                                             2.74                                 7     10:30:30:20:10                                                                              113     none  290, 400                                                                             2.48                                 8     20:30:25:10:15                                                                              113     none  160    2.10                                 9     20:30:25:5:20 122     none  163    1.76                                 10    35:35:15:10:5 107     179   135    4.14                                 11    30:40:15:10:5 107     190   145    3.30                                 12    20:40:20:15:5 109     226   125    3.34                                 13    30:30:20:15:5 109     233   155    2.68                                 14    20:30:25:20:5 112     301   250    3.93                                 ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Example   HBA:HNA:TA:BP:R:X                                                                             X                                                   ______________________________________                                        15        25:35:20:--:--:20                                                                             Phenyl hydroquinone                                 16        30:30:20:--:--:20                                                                             Phenyl hydroquinone                                 17        30:30:20:20:--:10                                                                             Phenyl hydroquinone                                 18        30:30:20:--:10:10                                                                             Phenyl hydroquinone                                 19        30:30:20:7:7:6  Phenyl hydroquinone                                 20        25:35:20:--:--:20                                                                             Methyl hydroquinone                                 21        30:30:20:10:--:10                                                                             Methyl hydroquinone                                 22        30:30:20:--:10:10                                                                             Methyl hydroquinone                                 23        30:30:20:5:10:5 Acetaminophen                                       ______________________________________                                    

Example 24

Preparation of Dye Blended COTBPR by Melt Blending:

60 grams of the COTBPR from Example 1and 0.3 gram of Methylene VioletBernthsen (from Aldrich Chemical Company, Milwaukee, Wis.) were chargedinto the mixing chamber of a Haake Mixer (Model No. 3042309, HBI System90, from Haake Company, Paramus, N.J.) . The mixing ball and itscontents were heated to 240° C. over about 30 minutes and then thecharge was blended at a rotational speed of 100 rpm for 15 minutes atthe temperature. The mixture of polymer and dye was removed from theball and allowed to cool to the ambient temperature.

Example 25

Extrusion of Film and Measurement of Polarizing Coefficient (PolarizingEfficiency):

20 grams of the dyed polyester from Example 24 was compacted into a rodof 3/8 inch diameter. The rod was charged into the melting section of amicro fiber spinning unit (designed internally by Hoechst CelaneseCorporation, Summit, N.J.). The polymer was melted and fed at a rate of0.56 g/minute into a melt chamber. A slit die was located at the end ofthe melt chamber through which the polymer melt was extruded. Thedimensions of the slit were 1/4 inch by 5 thousandths of an inch. Theextruding film was taken up by a take-up roll. During the spinning, theheater temperature was maintained at 230° C., the melt chambertemperature at 230° C. and the die temperature 235° C. The take-up speedof the film was 5 m/minute. The melt drawdown ratio, defined as theratio of the take-up speed to the exit speed of the extruding film atthe die exit, was 9. The width of the tape was 0.2 inches and thethickness 0.5 thousandths of an inch.

The obtained polarizing film had a blue color, a transmittance of 40%and a polarizing coefficient of 93% for the light in the wavelengthregion 550-630 nm, as measured following the procedure detailed in U.S.Pat. No. 5,071,906 cited above.

Example 26

Measurement of Thermal and Hygroscopic Stability:

The polarizer film from Example 25 was allowed to stand in atemperature-humidity-controlled oven at 100° C. and 95% R.H. for 120hours and the polarizing coefficient was determined again similarly. Thepolarizing coefficient was found to be 92%, showing little change.

For comparison, the polarizing coefficients of two commerciallyavailable polarizing films, one based on PVA film and iodine(NPF-G1220DV from Nitto Denko Corporation, Japan) and the other based onPVA and a dichroic dye (NPF-Q-12 from Nitto Denko Corporation), weresimilarly determined. The two commercial films initially had polarizingcoefficients of 99.95% and 88% respectively. After being allowed tostand in a temperature-humidity-controlled oven at 100° C. and 95% R.H.for 120 hours, the films showed significantly lowered polarizingcoefficients of 0% and 40%, respectively, demonstrating thereby that thepolarizer films of the present invention underwent far less, almostnegligible, degradation in their polarizing coefficient at 100° C. and95% R.H., compared with conventional polarizing films, indicative oftheir exceptional thermal and hygroscopic stability.

What is claimed is:
 1. An all organic polarizer film comprising a blendof (a) at least one film-forming, wholly aromatic thermotropic liquidcrystalline polyester and (b) at least one organic dichroic dye, andpossessing an initial polarizing efficiency of at least 70%, wherein thepolarizer film retains at least 90% of its initial polarizing efficiencywhen exposed to at least 90° C. temperatures and at least 90% RelativeHumidity for a period of at least 100 hours, further wherein saidpolyester comprises repeat units corresponding to the formula;

    -- P.sup.1 !.sub.m-- P.sup.2 !.sub.n -- P.sup.3 !.sub.q -- P.sup.4 !.sub.r -- P.sup.5 !.sub.s --

wherein P¹, P², P³, P⁴ and P⁵ represent monomeric moieties with P¹ beingan aromatic hydroxy carboxylic acid, P² being an aromatic dicarboxylicacid, P³ being a phenol, P⁴ being a second aromatic hydroxy carboxylicacid moiety different from P¹, and P⁵ being a second phenolic moietydifferent from P³, with m, n and q representing mole percent of therespective monomers ranging from 5-70 mole percent individually, andwith r and s representing mole percent of the respective monomersrespectively, r and s being 5-20 mole %.
 2. The polarizer film of claim1, wherein P¹ is selected from the group consisting of 4-hydroxybenzoicacid, 2-hydroxy-6-naphthoic acid, and4-carboxy-4'-hydroxy-1,1'-biphenyl.
 3. The polarizer film of claim 1,wherein P² is selected from the group consisting of terephthalic acid,isophthalic acid, phthalic acid, 2-phenylterephthalic acid,1,2-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid,2,6-naphthalene dicarboxylic acid and 4,4'-biphenyldicarboxylic acid. 4.The polarizer film of claim 1, wherein P³ is selected from the groupconsisting of resorcinol, hydroquinone, catechol,4,4'-dihydroxybiphenyl, 1,4-dihydroxynaphthalene,2,6-dihydroxynaphthalene and acetaminophen.
 5. The polarizer film ofclaim 1, wherein P⁴ is selected from the group consisting of4-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, and4-carboxy-4'-hydroxy-1,1'-biphenyl.
 6. The polarizer film of claim 1,wherein said P⁵ is a diphenol selected from resorcinol, hydroquinone,methyl hydroquinone, phenyl hydroquinone, catechol,4,4'-dihydroxybiphenyl, bisphenol A, and acetaminophen.
 7. The polarizerfilm of claim 2, wherein P¹ is 4-hydroxybenzoic acid.
 8. The polarizerfilm of claim 2, wherein P¹ is 2-hydroxy-6-naphthoic acid.
 9. Thepolarizer film of claim 3, wherein P² is terephthalic acid.
 10. Thepolarizer film of claim 4, wherein P³ is resorcinol.
 11. The polarizerfilm of claim 4, wherein P³ is 4,4'-dihydroxybiphenyl.
 12. The polarizerfilm of claim 5, wherein P⁵ is resorcinol.
 13. The polarizer film ofclaim 1, wherein said dye is selected from the group consisting ofstraight chain dye, branched dye, direct dye, disperse dye, solvent dyeand acidic dye.
 14. The polarizer film of claim 1, wherein said dye isselected from the group consisting of azo dyes, anthraquinone dyes,Disperse Red, Blue 214, Red 60 and Yellow 56, Black 17, 19 and 154,Brown 44, 106, 195, 210, 242 and 247, Blue 1, 15, 22, 78, 90, 98, 151,168, 202, 236, 249, and 270, Violet 9, 12, 51, and 98, Green 1 and 85,Yellow 8, 12, 44, 86, and 87, Orange 26, 39, 106 and 107, and Methyleneviolet Bernthsen.
 15. The polarizer film of claim 14, wherein said dyeis an anthraquinone dye.
 16. The polarizer film of claim 1, wherein saidblend is formed from said liquid crystalline polymer and said dye atabout 170° C.
 17. The polarizer film of claim 1, wherein said blend isformed from said liquid crystalline polymer and said dye at about themelt temperature of said polymer.
 18. The polarizer film of claim 17,wherein said blend is further extruded at about the melt temperature ofsaid liquid crystalline polymer to form the polarizing film.
 19. An allorganic polarizer film with high thermal and hygroscopic stability,comprising a blend of (a) a thermotropic liquid crystal polymer whichcomprises 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid,terephthalic acid, 4,4'-dihydroxybiphenyl and resorcinol in a molarratio 30:30:20:10:10 respectively, and (b) an organic dichroic dye, andpossessing an initial polarizing efficiency of at least 70%, wherein thepolarizer film retains at least 90% of its initial polarizing efficiencywhen exposed to at least 90° C. temperatures and at least 90% RelativeHumidity for a period of at least 100 hours.
 20. An all organicpolarizer film comprising a blend of (a) at least one film-forming,wholly aromatic thermotropic liquid crystalline polyesteramide and (b)at least one organic dichroic dye, and possessing an initial polarizingefficiency of at least 70%, wherein the polarizer film retains at least90% of its initial polarizing efficiency when exposed to at least 90C.temperatures and at least 90% Relative Humidity for a period of at least100 hours, further wherein said polyesteramide comprises repeat unitscorresponding to the formula:

    -- P.sup.1 !.sub.m-- P.sup.2 !.sub.n -- P.sup.3 !.sub.q -- P.sup.4 !.sub.r -- P.sup.5 !.sub.s --

wherein P¹, P², P³, P⁴ and P⁵ represent monomeric moieties with P¹ beingan aromatic amino carboxylic acid, P² being an aromatic dicarboxylicacid, P³ being a phenol, P⁴ being an aromatic hydroxy carboxylic acid,and P⁵ being a second phenolic moiety different from P³, with m, n and qrepresenting mole percent of the respective monomers ranging from 5-70mole percent individually, and with r and s representing mole percent ofthe respective monomers, r and s being 5-20 mole %.
 21. The polarizerfilm of claim 20, wherein P¹ is 4-aminobenzoic acid.